The Relationship between Waist Circumference and Work-related ...

Kim et al. Annals of Occupational and Environmental Medicine 2013, 25:29 http://www.aoemj.com/content/25/1/29

RESEARCH ARTICLE

Open Access

The Relationship between Waist Circumference and Work-related Injury in Reference to the Fourth Korea National Health and Nutrition Examination Survey Sung-Kyung Kim1, Ji-Min Son1, Jae-Young So1, Hyocher Kim2, Kyungsuk Lee2, Sung-Soo Oh1 and Sang Baek Ko1*

Abstract Objective: This study aims to investigate the relationship between waist circumference and work-related injury in reference to the fourth Korea National Health and Nutrition Examination Survey. Methods: By analyzing data from the fourth Korea National Health and Nutrition Examination Survey conducted from 2007 to 2009, we estimated the rate of injury experience according to socioeconomic status, including occupational property, of 8,261 subjects. We performed logistic regression analysis with work-related injury experience rate as dependent variable and waist circumference as an independent variable, Odds ratios (OR) were calculated, which reflect the likelihood of work-related injury experience rate, and 95% confidence interval (95% CI) while controlling for relevant covariates with stratifying by sex, age, nature of injury, site of injury and occupational group. Results: Among 797 persons who had injury experience over the past 1 year, 293 persons (36.8%) had work-related injury experience. After adjusting the confounding variables, the work-related injury was related to abnormal waist circumference (OR = 1.35; 95% CI: 1.02 ~ 1.78). In subgroups, ORs were higher in men (OR = 1.42; 95% CI: 1.02 ~ 1.98), professional, manager, and administrator (OR = 2.41; 95% CI: 1.10 ~ 5.28). Higher rate of injuries were noted in back and waist (OR = 2.92; 95% CI: 1.49 ~ 5.73), and transport accident had increased risk (OR = 1.60; 95% CI: 1.13 ~ 2.28). Conclusions: Work-related injury rate differed depending on the waist circumference. The abdominal obesity was associated with higher risk of work-related injury. This study would be useful in selecting appropriate priorities for work-related injury management in Korea. Keywords: Work-related injury, Waist circumference, Risk factors

Introduction Based on 2011 department of Korea statistics, generalized improvement in nutrient intake by Korean population has raised the rate of obesity. The rate was found to be higher in men (36.5%) than women (26.5%) [1]. Obesity has a well-known association to raise the prevalence of cardiovascular disease or type 2 diabetes [2,3]. Also, it is known that obese person is more likely to have sprain or dislocation injury than non-obese person [4], and risk of fracture is affected by the obesity. For a person with * Correspondence: [email protected] 1 Department of Occupational and Environmental Medicine, Wonju Severance Christian’s Hospital, Yonsei University, Wonju, Korea Full list of author information is available at the end of the article

body mass index (BMI) between 25 and 29.9 kg/m2, the fracture risk is 1.29 times higher than a person with BMI of 29.9 kg/m2. People with BMI of between 30 and 34.9 kg/m2 and between 35 and 39.9 kg/m2 had increased risks of 1.67 and 1.94 times, respectively, revealing significant increase in fracture risk with higher BMI [5]. Injury is disability of body caused by external factors, and injuries originate during work is defined as workrelated injury [6]. In Korea, Industrial Accident Compensation Insurance Act states that occupational casualty is any injury, disease, disability, or death of a worker from causes originating or relating to his or her occupation [7]. These casualties are attributed by accidents or noxious agents including physical factors, chemical materials,

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dusts, pathogens, works that put excessive strain to body. Conventionally, exposure to physical and chemical harmful agents and unsafe behavior are explained to be major sources of work-related injury [8,9]. Occupation injury leads to pathologic condition, disability, and early mortality, and in turn, these losses translate into loss of life expectancy and increased cost in a society [10,11]. Since 2001, applicant to occupational health and safety insurance had become widespread. The number of work places that had applied for the insurance has increased by 41.7% in 2009 from 2001, and 23.8% increase in full-time workers was noted during the same period. However, these years had shown steady increase of injured workers. For workrelated accident, less mortality became evident in recent years, but the number of injured persons increased every year. Rate for work place accident momentarily had increased from 2003 to 2004, but in general, the figure has stagnated or decreased at around 0.7% [12]. Injury is no longer recognized as random and unavoidable accident, but its perception has become preventable accident. Thus several nations are attempt in to set up an effectual policy for reduction of the injury, and collecting injury-related data to produce base reference in developing a policy is identified as an important agenda [13]. It is known that work-related injury and disease originate through complex interaction of several risk factors [14-16]. Recently, some claimed that obesity function as a protective factor in injury [17], but obesity is generally considered as a risk factor [18]. Body mass index (BMI) was used in several studies to define obesity. However, the index has been acknowledged inappropriate to reflect fluctuation of body fat distribution and different characteristics in obesity among individuals and population groups. In some cases, BMI is mainly attained from records that subjects had recorded for themselves rather than measuring the index for examination. This lowers validity of the data and showed inconsistency of outcomes [19,20]. Because measuring abdominal fat is known to have more sensitivity in detecting individual differences than BMI, it is more useful to discover risk factors of obesity-related disease [19,21]. There have been studies to identify obesity’s relationship to injury in a work environment, and they reported that obese persons have about 26 to 107% more incidence of injury during working than people with normal weight [14,22-24]. They in addition noted that higher BMI showed increased frequency of acute traumatic injury at work [23,25]. However, these studies used BMI only to investigate the relationship until now. As mentioned above, waist circumference has become recognized as a more useful index than BMI to study health problem associated with obesity [19,21,26], but few reports have been made about relationship between workrelated injury and obesity using waist circumference.

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In addition, it is still unclear about abdominal obesity’s mechanism and extent to injury. Thus, it necessitates investigation and discussion about its role as a factor that incites injury [27]. In this study, its purpose is to determine relationship between waist circumference and work-related injury. The authors want to apply outcomes found in this study to manage obesity for prevention of injury at work.

Materials and methods Study subjects

The Korea National Health and Nutrition Examination Survey has been performed to identify Korean health and nutrition state since 1998. The fourth Korea National Health and Nutrition Examination Survey was conducted for 3 years from 2007 to 2009 with rolling survey sampling method. Each rolling sample was extracted from the survey, and it was designed to have independent and identical properties among samples. Year-round survey (50 weeks per year) was conducted, and 200 to 250 subjects were surveyed in a week. In each year, probability samples reflecting the whole country were extracted through stratified sampling in 3 stages. First stage involved stratification of 29 strata with a reference to 11 areas’ population ratio by sex and age groups, and the samples were collected according to towns. Second stage extracted samples at district level, and final stage collected samples in family level. Number of participation to the survey was 23,632 (74.5%) among 31,705 national wide subjects [28]. Final analysis was done to 8,261 adults between 20 and 65 years old who had an experience of injury in his or her job. Study methods

In this study, work-related injury was defined as an experience of injury for the past 1 year from the time of the fourth Korea National Health and Nutrition Examination Survey. Those who had answered yes to a question “have you received a treatment in a hospital or emergency room due to injury or intoxication?” were reviewed, and among them people who answered yes to “during work” in additional information section were finally defined as a work-related injury experiment [29]. As demographic and socioeconomic characteristics, age, sex, waist circumference, alcohol intake, smoking state, exercise level, marital status, annual household income, and educational level were identified. Also, mechanism of injury and injury site were noted. We organized occupations into 6 groups according to major categorizations of the ‘6th Korean Standard Classification of Occupations’; ‘manager, professional, and administrator’, ‘clerk’, ‘service and sales worker’, ‘skilled agricultural, forestry, and fishery worker’, ‘craft, equipment, machine operating, and assembling worker’, and ‘elementary worker’ [29]. Abdominal obesity is termed for man with waist circumference of


90 cm or above and woman with the circumference of 85 cm or above [30]. In this study, injury rates were calculated according to demographic and occupational characteristics of study subjects. Also, injury experience was set as a dependent variable, and abdominal obesity was used as an independent variable. Using the variables, logistic regression analysis was performed to calculate corrected odds ratio (OR) of work-related injury experience to population and 95% confidence interval (CI). Stratified analysis was carried out for age, sex, injury mechanism, injury site, and occupational groups. SAS 9.2 program (SAS Inc., Cary, NC, USA) was used for statistical analysis, and statistical significance was determined at 0.05 or below.

Results General and occupational characteristics of study subjects

Table 1 listed general and occupational characteristics of study subjects. Male consisted 55.4% of total subjects, and age with 40 or above accounted 58.8%. Waist circumference was within the normal range for 6,093 subjects (74.1%) and above the normal range for 2,179 subjects (25.9%). For male, there were 27.7% of study subjects who had waist circumference of 90 cm or above, and for female, the proportion with abnormal waist circumference was 24.7%. Percentage of people who had suffered an injury over the 1 year was 7.2%, and 3.3% of study subjects had sustained their injuries from work. There were 23% of population working in ‘service and sales worker’ group, and next was followed by ‘manager, professional, and administrator’ group with 20.9%, ‘craft, equipment, machine operating, and assembling worker’ group had 18% of population working for the sector, Proportions for ‘elementary worker’ group and ‘clerk’ group were 13.7% and 13.6%, respectively. ‘Skilled agricultural, forestry, and fishery worker’ group had the least figure of 10.8% working in the sector. For injury mechanism, motor vehicle accident (43.3%) was found to be the most common cause. Fall, slip down, and collision were found in 35.4%, and laceration, amputation, stab, and injured by machine were identified in 14.4% as their injury mechanisms, Burn and intoxication were answered by 3.4% of study subjects. Unknown and other causes were noted in 3.4%. Subjects had fairly even distribution on sites of their injuries. Head, face, and neck were injured in 24.5%. Back and waist were affected in 27.5%, and upper and lower extremities were answered as their injury site in 23.8% and 21.8%, respectively. Risk of work-related injury regarding to waist circumference

As listed in Table 2, multiple logistic regression analysis showed that work-related injury was 1.49 times (95% CI: 1.16 ~ 1.92) higher in abnormal waist circumference group than within normal waist circumference group.

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After correcting confounding variables, work-related injury was discovered to 1.35 times (95% CI: 1.02 ~ 1.78) higher in the abnormal group. Factors related to work-related injury in abnormal waist circumference group

Stratified multiple logistic regression analysis was made on age, sex, occupational groups, injury sites, and mechanism, and male with abnormal waist circumference had 1.42 times higher risk of injury during work (95% CI: 1.02 ~ 1.98). For ‘Manager, professional, and administrator’ group, the risk of work-related injury was 2.41 times higher (95% CI: 1.10 ~ 5.28) in people with abnormal waist circumference. The abnormal waist circumference group was 2.92 times higher risk of thoracic and lumbar spine injuries (95% CI: 1.49 ~ 5.73). Motor vehicle accident also showed significant increase in risk by 1.60 times (95% CI: 1.60 ~ 1.98) (Table 3).

Discussion This study investigated relationship between work-related injury and waist circumference. Subjects were selected using the 4th Korea National Health and Nutrition Examination Survey, and those who had experienced an injury over 1 year period were accounted for the study. There were 7.2% of patients who suffered injury over 1 year, and injuries that were related to work was 3.3% of the population. Waist circumference was measured to each subject to evaluate obesity, 74.1% were found to be within normal range. There were 27.7% of male population who had abnormal waist circumference, and 24.7% of female subjects had abdominal obesity. Young age, short work experience, male, improper education about health and safety, insomnia, and work stress are known to have significant relationship with workrelated injury [14,17,31,32]. Recently, obesity has been recognized as a risk factor of injury [14,33]. In this study, multiple logistic regression analysis showed that age, sex, exercise, smoking, alcohol intake, marital status, and occupations had 1.35 times higher risk of work-related injury (95% CI: 1.02 ~ 1.78). Also, in the group who are male, who had abnormal waist circumference, motor vehicle accidents, and managerial and professional jobs, and whose injury sites were back and waist illustrated significant relationship with work-related injury. This study used waist circumference instead of BMI to determine obesity, because waist circumference is suggested by several studies to more indicative of obesity than BMI [26]. However, previous studies that studied relationship between obesity and work-related injury had used BMI as index for obesity [14,33]. In addition, reports were published concerning obesity as both hazard and protective factor in work-related injury [17]. It is considered as a risk factor because over-weight


Table 1 General characteristics of participants Variables

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Table 1 General characteristics of participants (Continued)

Prevalence (%)

Married, living

77.0

Male

55.4

Married, separated

1.8

Female

44.6

Bereavement

2.7

Age

20 ~ 40y

41.2

Divorce

3.6

41 ~ 65y

58.8

Single

14.5

Waist circumference

Male < 90 cm

72.3

Unknown

0.3

Male ≥ 90 cm

27.7

≥Moderate

29.1

Female < 85 cm

75.3